14
2. Multiple Dryer (Common) Venting
If it is not feasible to provide separate exhaust ducts for each dryer, ducts from individual dryers may be
channeled into a common main duct. The individual ducts should enter the bottom or side of the main duct
at an angle not more than 45º in the direction of the airflow.
IMPORTANT:
No more than eight (8) dryers
should be
connected to one (1) main common duct.
NOTE:
Refer to the
illustration
on
page 15
for examples of multiple dryer (common) venting.
The main duct may be any shape so long as the minimum cross-sectional area is provided. The
illustration
on
page 15
shows the minimum cross-sectional area for multiple dryer venting. These figures
must be
increased in proportion if the main duct run from the last dryer to where it exhausts to the outdoors is
unusually long (over 20 feet [6.1 meters]) or has numerous elbows (more than one [1]) in it.
IMPORTANT:
For extended duct work runs, the cross-sectional area of the duct work can only be
increased to an extent. Maximum proportional duct work runs
cannot
exceed 20 feet
(6.1 meters) more than the original limitations of 20 feet (6.1 meters) with one (1)
elbow. When the duct work approaches the maximum limits as noted in this manual, a
professional heating, venting, and air-conditioning (HVAC) firm
must be
consulted for
proper venting information.
IMPORTANT:
Exhaust back pressure measured by a manometer at the dryer’s exhaust duct area
must not exceed
0.3 inches of water column (W.C.) - 0.74 mb - when both baskets
(tumblers) are operating.
The duct work
should be
smooth inside with no projections from sheet metal screws or other obstructions
which will collect lint. When adding ducts, the duct to be added should overlap the duct to which it is to be
connected.
ALL
duct work joints
must be
taped to prevent moisture and lint from escaping into the
building. Also, inspection doors
should be
installed at strategic points in the exhaust duct work for periodic
inspection and cleaning.
NOTE:
When the exhaust duct work passes through a wall, ceiling, or roof made of combustible
materials, the opening
must be
2-inches (5.08 cm) larger than the duct (
ALL
the way around).
The duct
must be
centered within this opening.
To protect the outside end of the horizontal duct work from the weather, a 90º elbow bent downward
should
be
installed where the exhaust exits the building. If the exhaust duct work travels vertically up through the
roof, it
should be
protected from the weather by using a 180º turn to point the opening downward. In either
case, allow at least twice the diameter of the duct between the duct opening and nearest obstruction.
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